The objective of this project is to isolate Herpes simplex virus coded functions required for viral DNA replication. Two cell-free DNA synthesis systems have been developed capable of synthesizing viral DNA. Several of the viral mutants temperature sensitive for viral DNA synthesis after infection of cells in culture show temperature-sensitive defects during synthesis in the cell-free system. It is planned to develop purification of the affected functions. In addition, cell-free DNA synthesis systems from wild-type infected cells will be used to study the detailed mechanism of Herpes virus DNA replication.